Multichannel microwave filter

ABSTRACT

Filter miniaturization is achieved by utilizing a dielectric resonator as the resonant circuit in each individual filter of a multichannel microwave filter bank. The filter circuits are mutually isolated and compactly stored in a multiple compartment filter housing structure. The housing structure consists of a center conductor, multiple conductive sheet members spaced transversely along the center conductor and multiple conductive sheet members parallel to and radiating from the center conductor. All conductive sheet members are interlocked to form a multiplicity of individual compartments that envelope the center conductor. The center conductor and the proximal edges of the parallel conductive sheet members define a coaxial microwave transmission line from which input microwave signal energy is coupled by means of coupling loops or probes to each individual filter circuit.

United States Patent [191 Lammers et al.

[451 Mar. 25, 1975 MULTICHANNEL MICROWAVE FILTER [73] Assignee: The United States of America as represented by the Secretary of the United States Air Force, Washington, DC.

[22] Filed: Feb. 4, 1974 [21] Appl. No.: 439,670

52 us. Cl. 333/73 (3, 333/83 R, 333/84 R, 333/96, 333/97 R 511 rm. Cl H0lp 3/06, HOlp 7/04, HOlp 7/06 [58] Field of Search... 333/70 s, 73 c, 73 R, 82 B, 333/82 R, 83 R, 84 R, 84 M, 96, 97 R;

[56] References Cited UNITED STATES PATENTS 2,838,736 6/1958 Foster 333/83 R 2,890,422 6/1959 Schlicke 333/83 R X 3,742,390 6/1973 Stiglitz et al. 333/83 R X Primary Examiner-James W. Lawrence Assistant Examiner-Marvin Nussbaum Attorney, Agent, or Firm-Harry A. Herbert, .lr.; Willard R. Matthews, Jr.

[ ABSTRACT Filter miniaturization is achieved by utilizing a dielectric resonator as the resonant circuit in each individual filter of a multichannel microwave filter bank. The filter circuits are mutually isolated and compactly stored in a multiple compartment filter housing structure. The housing structure consists of a center conductor, multiple conductive sheet members spaced transversely along the center conductor and multiple conductive sheet members parallel to and radiating from the center conductor. All conductive sheet members are interlocked to form a multiplicity of individual compartments that envelope the center conductor. The center conductor and the proximal edges of the parallel conductive sheet members define a coaxial microwave transmission line from which input microwave signal energy is coupled by means of coupling loops or probes to each individual filter circuit.

3 Claims, 3 Drawing Figures MULTICHANNEL MICROWAVE FILTER BACKGROUND OF THE INVENTION This invention relates to multichannel microwave filter banks, and in particular to the use of dielectric resonators in microwave filter circuits and to structures for mutually isolating and compactly packaging such circuits.

It is a common objective of designers of communications, radar and electronic countermeasures systems, to achieve effective shielding and component isolation while simultaneously reducing size and weight requirements. This is especially true when these systems are used in airborne or space applications. The use of large microwave filter banks in such systems has in the past required relatively complex circuitry and'substantial space has been used to ensure effective channel isolation. There currently exists, therefore, the need for construction means and circuit designs that permit the fabrication of large microwave filter banks with maximum channel isolation while maintaining minimum space requirements and minimum circuit complexity.

SUMMARY OF THE INVENTION The present invention comprehends a multichannel filter structure which can be used to feed and mutually shield a large number of microwave dielectric resonator filters with minimum space requirement. The filters are arranged around and along a common feedline. This feedline represents the center conductor of a coaxial transmission line, which is properly terminated at one end. The center conductor is concentrically surrounded by a multicavity structure, which houses the microwave filters in individual shielded compartments and simultaneously acts as the outer coaxial conductor. Coupling loops extending from these compartments into the transmission line couple a sample of the RF power to each of the dielectric resonators. At resonance this power passes through the resonator into a second coupling loop where it is detected by a diode circuit.

It is a principal object of the invention to provide a new and improved multichannel microwave filter.

It is another object of the invention to provide a new and improved microwave filter circuit utilizing a dielectric resonator.

It is another object of the invention to provide a new and improved multichannel microwave filter housing structure.

It is another object of the invention to provide a multi-channel microwave filter bank that has maximum channel isolation and that requires minimum space and circuit complexity.

These, together with other objects, features and advantages of the invention, will become more readily apparent from the following detailed description when taken in conjunction with the illustrative embodiment in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of the microwave filter housing structure comprehended by the invention;

FIG. 2 is a partially cut-away isometric view of one compartment of the multichannel microwave filter comprehended by the invention; and

FIG. 3 is a schematic diagram of the microwave filter circuit of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Some types of microwave filters, particularly dielectric resonator filters, require minimum space, and are therefore well suited to implement large bandwidth filter banks. The multi-channel microwave filter housing structure of the present invention illustrated in FIG. 1 is designed to efficiently preserve the size advantage of this type of filter element in a multiple filter arrangement. It comprises a section of coaxial transmission line, where the outer structure houses the microwave filters and simultaneously acts as the outer coaxial conductor. It is assembled from m circular metal partitions 4 and n rectangular metal partitions 5 to make up a (m-l)n compartment cylinder. One of the rectangular partitions 5 has been removed in FIG. 1 to show how both types of partitions are slotted to fit together. The cylindrical structure has an axial hole 15 extending over its total length. The center conductor 6 is concentrically held within the axial hole by means ofinsulating bushings (not shown). For sufficiently thin partitions the'outside wall of the center hole of the cylindrical structure exists only partially, leaving one rectangular inner opening 14in each of the (m-l )n compartments. The ratio of the hole diameter (outer coaxial conductor) and the inner coaxial conductor diameter is chosen to obtain a suitable characteristic impedance of the transmission line.

The dielectric resonators are disks of single crystalline materials, such as SrTiO CaTiO and others, as well as ceramic oxide and titanate compounds, such as the temperature compensated Barium Tetrate Titanatc material. When these high dielectric, low loss materials are designed properly, they will act as resonant microwave filters, much as a hollow metal cavity does when excited by a microwave signal of its resonant frequency.

FIG. 2 illustrates the physical layout of the microwave filter circuitry that is contained in each of the (m-l)n compartments, and FIG. 3 the corresponding schematic diagram. Coupling from the feedline (that is, the microwave transmission line defined by conductor 6 and the proximal edges of partitions 5) to the resonator and from the resonator to the detection circuit is accomplished by proper linking of the RF magnetic field lines. The coupling and detection circuits are .etched and mounted on a low loss microstrip board 12 which also holds the dielectric resonator 8. Coupling loop 7 extends through inner hole 14 of the compartment into the transmission line field. An RF current is thus induced in loop 7 by the transmission line field. The field thus generated in loop 7 in turn excites dielectric resonator 8. At resonance, power is coupled through the resonator 8 into the second loop 9 and is detected in the microwave diode l0. Resistor 11 represents a resistive load, which is required for properly shaping the filter response. The position of the individual microstrip filter/detector boards 12 is adjustable within the compartments by means of screw 13 in order to optimize the coupling and for minor frequency correction. The width of the microstrip conductors, the thickness of the boards and the dielectric constant of the substrate material are determined by standard microstrip circuit techniques.

While the invention has been described in its preferred embodiment, it is understood that the words which have been used are words of description rather than words of limitation and that changes may be made within the purview of the appended claims without departing from the scope and spirit of the invention in its broader aspects.

What is claimed is:

l. A multichannel microwave filter housing structure comprising a conductor,

a plurality of conductive sheet members transversely partitioning said conductor into sections, and

a plurality of conductive sheet members disposed parallel to and extending radially from a proximate radial locus about said conductor,

said transverse and parallel sheet members being engaged to define a multiplicity of compartments, and said conductor and the proximal edges of said parallel sheet members cooperating to define a coaxial transmission line.

2. A multichannel microwave filter comprising a conductor,

a plurality of conductive sheet members transversely partitioning said conductor into sections,

a plurality of conductive sheet members disposed parallel to and extending radially from a proximate radial locus about said conductor, said transverse and parallel sheet members being engaged to define a multiplicity of compartments, and said conductor and the proximal edges of said parallel sheet members cooperating to define a coaxial transmission line, and

a microwave filter circuit disposed in at least some of said compartments.

3. A multichannel microwave filter as defined in claim 2 wherein each said microwave filter circuit comprises a dielectric resonator,

an input coupling loop adapted to couple electromagnetic wave energy from said coaxial transmission line to said dielectric resonator,

a diode detector, and

means for inductively coupling said dielectric resonator and said diode detector. 

1. A multichannel microwave filter housing structure comprising a conductor, a plurality of conductive sheet members transversely partitioning said conductor into sections, and a plurality of conductive sheet members disposed parallel to and extending radially from a proximate radial locus about said conductor, said transverse and parallel sheet members being engaged to define a multiplicity of compartments, and said conductor and the proximal edges of said parallel sheet members cooperating to define a coaxial transmission line.
 2. A multichannel microwave filter comprising a conductor, a plurality of conductive sheet members transversely partitioning said conductor into sections, a plurality of conductive sheet members disposed parallel to and extending radially from a proximate radial locus about said conductor, said transverse and parallel sheet members being engaged to define a multiplicity of compartments, and said conductor and the proximal edges of said parallel sheet members cooperating to define a coaxial transmission line, and a microwave filter circuit disposed in at least some of said compartments.
 3. A multichannel microwave filter as defined in claim 2 wherein each said microwave filter circuit comprises a dielectric resonator, an input coupling loop adapted to couple electromagnetic wave energy from said coaxial transmission line to said dielectric resonator, a diode detector, and means for inductively coupling said dielectric resonator and said diode detector. 